Disentangling the complex spectrum of the ethynyl cation

Abstract

Ethynyl cation, C2H+, is of great importance in astrophysical media and in combustion. It is involved in the formation of larger organic compounds and on their decomposition mechanisms. Here, we investigate the low lying electronic states of this cation using pure ab initio methodologies. Evolutions of its potential energy surfaces along the stretching and bending coordinates reveal a high density of electronic states that favours their mutual interactions and the mixing of their wavefunctions. The ground state is of 3Π space symmetry and the lowest singlet state (1Π) is found to be a quasi-linear – quasi-linear Renner-Teller system. Reproducing the (spin-)rovibronic spectra of such a molecular system to facilitate its detection is notoriously a complicated task, because of the multiple couplings, including Renner-Teller, vibronic, spin-orbit, that have to be included in the description. In sum, our work shows that the ethynyl cation, in spite of its small size, still represents a challenging molecular problem to be solved.

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